Inspection method and inspection apparatus of reinforced concrete pipe

ABSTRACT

Deterioration of reinforced concrete pipes is checked and the deterioration progress level is classified. Based on the inspection result, a portion to be inspected in detail in an inspection area is selected. With respect to the selected portion to be inspected in detail, the pipe thickness and the diameter of reinforcing bars are measured and the location of reinforcing bars in the portion to be inspected in detail are checked. Using the data of the thickness of a pipe, the diameter of the reinforcing bar and disposition of the reinforcing bars, structural analysis is carried out and the strength of the reinforced concrete pipe is calculated. The calculation result is used as information for evaluating the deterioration state of the reinforced concrete pipe.

This application is a divisional of U.S. application Ser. No.10/513,698, filed Nov. 8, 2004, now U.S. Pat. No. 7,360,462 which is anational stage application of International Application No.PCT/JP03/04587, filed Apr. 10, 2003, now allowed.

TECHNICAL FIELD

The present invention relates to an inspection method and an inspectionapparatus for inspecting the deterioration state of reinforced concretepipes.

BACKGROUND ART

Conventionally, in a sewage conduit and irrigation conduit, manyreinforced concrete pipes (Hume pipe) are used.

In sewage and irrigation conduits built using reinforced concrete pipes,due to corrosion, abrasion and breakage caused from aging of concretepipes, problems such as cave-in and water leakage have been increasing.Therefore, appropriate repair and renewal thereof based on appropriatediagnosis of the deterioration and the inspection result thereof arerequired.

In the diagnosis and inspection of the sewage and irrigation conduits,generally, in order to determine the order and construction method ofrepair and renewal work, it is required to classify the progressionlevel of deterioration in a component segment constituting the drainagebasin to be inspected, and it is necessary to detect the progressionlevel of the deterioration in a quantitative manner.

Conventionally, in general, such a method, in which a visual check andan appearance inspection are carried out using a TV camera; and ifnecessary, a core is taken out to inspect solid state propertiesthereof, is carried out.

However, in the above-mentioned technique, only visible deteriorationcan be detected; accordingly, deterioration on the periphery and insideof the pipe cannot be detected. Additionally, it is impossible to detectthe progression level of deterioration in an appropriate andquantitative manner, and it is necessary to take out a large amount ofcores to collect quantitative data. Therefore, there arise such problemsthat the strength of the sewage or irrigation conduit is reduced, andsignificant manpower is required.

On the other hand, it has been considered to put the inspection methodsused for concrete structures into use.

For example, systems, in which the width and depth of cracks areestimated using elastic waves, have been disclosed in Japanese PublishedUnexamined Patent Application No. H10-142200 and Japanese PublishedUnexamined Patent Application No. H09-269215. However, these systems arenot satisfactory in workability. When these systems are applied to theinspection of a structure extending over a long distance such as sewageand irrigation conduits, it takes a considerably long time for theinspection.

The present invention has been proposed to solve the above-describedproblems. It is an object of the present invention to provide aninspection method for reinforced concrete pipes which, when inspectingthe deterioration state of a reinforced concrete pipe constituting asewage conduit, irrigation conduit or the like, is capable of increasingthe efficiency of the inspection work as well as evaluating theprogression level of deterioration in a quantitative manner, and aninspection apparatus suitable for carrying out such an inspectionmethod.

SUMMARY OF THE INVENTION

An inspection method according to the present invention is an inspectionmethod for reinforced concrete pipes for inspecting the deteriorationstate of a reinforced concrete pipe inside the pipe, which comprises aninspection step for checking the presence or absence of deterioration bycarrying out any one or both of a visual examination and impact elasticwave test and classifying the progression level of the deterioration; aninspection portion selecting step for selecting a portion to beinspected in detail in an inspection area based on the inspectionresult; a measuring step for measuring the pipe thickness and thediameter of reinforcing bars in the selected portion to be inspected indetail; a reinforcing bar disposition checking step for checking thelocation of the reinforcing bars in the portion to be inspected indetail; and a calculating step for calculating the strength of thereinforced concrete pipe by analyzing the structure using the respectivedata of the pipe thickness, the diameter of the reinforcing bars and thedisposition of the reinforcing bars obtained in those two steps. Thecalculation result obtained in the calculating step is used as theinformation for evaluating the deterioration state of the reinforcedconcrete pipe.

According to the inspection method of the present invention, since theprogression level of the deterioration of the component segment in thearea to be inspected is classified and the portion to be inspected indetail is selected, the inspection operation time can be reduced.Further, the progression level of the deterioration in the portion to beinspected in detail can be evaluated based on the strength of the pipein a quantitative manner.

In the inspection method according to the present invention, it may beadapted so that, in addition to the pipe thickness and the diameter ofthe reinforcing bars, the depth of cracks is measured in the measuringprocess.

Further either or both of the step for determining the deterioratedportion (position of cracks) and the step for measuring the strength ofconcrete may be added.

In the inspection method of the present invention, it is preferred tocarry out the measurement of the pipe thickness to be inspected, thedetermination of the deteriorated portion and the measurement of thedepth of cracks using an elastic wave transmitter and receiver.

The inspection method according to the present invention is aninspection method for reinforced concrete pipes for inspecting thedeterioration state of a reinforced concrete pipe inside the pipe, whichcomprises the steps of: measuring propagation waves of a pipe to beinspected by carrying out an impact elastic wave test; analyzing theresonant frequency spectrum of the propagation waves; and determiningthe deterioration level based on the area ratio between an area of ahigh frequency component and an area of a low frequency component in theresonant frequency spectrum.

The inspection method according to the present invention is aninspection method for reinforced concrete pipes for inspecting thedeterioration state of a reinforced concrete pipe inside the pipe, whichcomprises the steps of: measuring propagation waves of a pipe to beinspected by carrying out an impact elastic wave test; analyzing theresonant frequency spectrum of the propagation waves; and determiningthe deterioration level based on the strength ratio between the top peakstrength in the high frequency range (for example, frequency range of 4to 10 kHz) and the top peak strength in the low frequency range (forexample, frequency range 3 to 4 kHz) in the resonant frequency spectrum.

The inspection method according to the present invention is aninspection method for reinforced concrete pipes for inspecting thedeterioration state of a reinforced concrete pipe inside the pipe, whichcomprises the steps of measuring propagation waves of a pipe to beinspected by carrying out an impact elastic wave test; and determiningthe deterioration level based on the changes in the maximum amplitudevalue of the propagation waves. The wording “maximum amplitude value ofthe propagation wave” in the present invention means the magnitude atwhich the absolute value in the waveform data of the propagation wavesreaches the maximum value as shown in FIG. 16.

According to the respective inspection methods of the invention, thedeterioration level of a reinforced concrete pipe constituting a sewageconduit, irrigation conduit or the like can be determined in aquantitative manner.

The inspection method according to the present invention is aninspection method for reinforced concrete pipes for inspecting thedeterioration state of a reinforced concrete pipe inside the pipe, whichcomprises the steps of: measuring propagation waves by carrying out animpact elastic wave test; obtaining changes of maximum magnitude in thepropagation waves; calculating the area ratio between the area of thehigh frequency component and the area of the low frequency component inthe resonant frequency spectrum by analyzing the resonant frequencyspectrum of the propagation waves; and determining the classification ofdeterioration phenomenon and the deterioration progress level bycombining the changes of maximum amplitude value in the propagationwaves and the area ratio in the resonant frequency spectrum.

In the inspection method of the invention, it may be arranged so that astep for calculating the strength ratio between the top peak strength ina high frequency range and the top peak strength in a low frequencyrange of the resonant frequency spectrum is added, and the determinationis carried out while adding the top peak strength ratio to thedetermination criteria.

Also, it may be arranged so that, a step for calculating the changes indecay time of the propagation waves, and the determination is carriedout while adding the changes in decay time to the determinationcriteria.

The inspection method according to the present invention is aninspection method for reinforced concrete pipes for inspecting thedeterioration state of a reinforced concrete pipe inside the pipe bymeans of an impact elastic wave test. The impact elastic wave test iscarried out in a state in which the distance between the elastic waveinjecting position and the elastic wave receiving position is ¼ or moreof the length of the pipe to be inspected away from each other.

The reason why the disposition distance is prescribed is to clearlydetect the changes of the vibration mode. That is, when the distancebetween the elastic wave injecting position and the receiving positionis shorter than ¼ of the length of the pipe, the vibrations in the areaadjacent to the transmitter are detected too strongly. In addition, thechanges of the vibration mode due to the deterioration in a portion faraway from the elastic wave injecting position and the elastic wavereceiving position is received unclearly. By setting the distancebetween the elastic wave injecting position and the receiving positionto ¼ or more of the length of the pipe, the intended object can beachieved. More preferably, the distance is ⅓ or more of the length ofthe pipe.

The inspection method according to the present invention is aninspection method for reinforced concrete pipes for inspecting thedeterioration state of a reinforced concrete pipe inside the pipe bymeans of an impact elastic wave test. The impact elastic wave test iscarried out by using any one of a receiver of which the configuration ofthe front end is a cone-like shape or needle-like shape, a receiver ofwhich the front end surface is a flat surface and the area of the frontend surface is 3 cm² or less, or a receiver of which the front endsurface is a curved surface and the curvature radius of the front endsurface is 25 mm or less as the receiver of the elastic waves.

As described above, by controlling the configuration of the receiver,receiving failure of the impact elastic waves (propagation waves) due toa contact failure between the receiver and the pipe inner surface causedfrom adhered layers, decayed layers on the inner surface layer of thereinforced concrete pipe constituting the sewage conduit, irrigationconduit or the like, or unevenness of the surface due to exposedreinforcing bars caused from abrasion, can be eliminated. Accordingly,the accuracy of the test can be prevented from degrading.

An inspection apparatus according to the present invention is aninspection apparatus for reinforced concrete pipes used for inspectingthe deterioration state of a reinforced concrete pipe inside the pipe bymeans of an impact elastic wave test, which comprises: a trolley mountedwith a hammering unit; a trolley mounted with a receiving unit; and ajoint member for connecting the two trolleys at a specific distance.

The inspection apparatus according to the present invention may beadapted so as to determine an elastic wave injecting position andelastic wave receiving position by using a trolley mounted with a TVcamera.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an inspection process according to anembodiment of the present invention;

FIG. 2 is a diagram showing an example of a block to be inspected;

FIG. 3 is a perspective view showing a structural analysis model used inthe embodiment of the present invention;

FIG. 4 is a diagram showing a configuration data used for structuralanalysis;

FIG. 5 is a diagram showing a load-stress curve created in thestructural analysis;

FIG. 6 is a diagram for illustrating a sample T13 used in an example ofthe present invention;

FIG. 7 is a diagram showing a location of a measuring device on asample;

FIG. 8 is a diagram schematically showing a preparation step of a sampleused in an example of the present invention;

FIG. 9 is a diagram showing a location of measuring devices on a sample;

FIG. 10 is an illustration schematically showing a sample introducedwith axial cracks;

FIG. 11 are spectrum charts of resonant frequency of each sample;

FIG. 12 is a graph showing the frequency component ratio of each sample;

FIG. 13 is a diagram schematically showing a crack introducing methodemployed in an example of the present invention;

FIG. 14 is an illustration schematically showing a sample introducedwith a peripheral crack;

FIG. 15 are resonant frequency spectrum charts of each sample;

FIG. 16 is a diagram for illustrating a maximum amplitude value of apropagation wave;

FIG. 17 is a diagram for illustrating the decay time of a propagationwave;

FIG. 18 is a flowchart showing the steps in determination processing,which are applied to the embodiment of the present invention;

FIG. 19 is also a flowchart showing the steps in determinationprocessing;

FIG. 20 is also a flowchart showing the steps in determinationprocessing;

FIG. 21 is also a flowchart showing the steps in determinationprocessing;

FIG. 22 is also a flowchart showing the steps in determinationprocessing;

FIG. 23 is a graph showing the frequency component ratio of each sample;

FIG. 24 is a graph showing the frequency component ratio of each sample;

FIG. 25 are resonant frequency spectrum charts of each sample;

FIG. 26 are illustrations showing locations of a measuring device on asample;

FIG. 27 is a graph showing the relationship between the incidentposition-receiver distance and the maximum amplitude value of apropagation wave;

FIG. 28 are perspective views showing examples of receivers;

FIG. 29 are perspective views showing other examples of receivers;

FIG. 30 are perspective views showing other examples of receivers;

FIG. 31 is a diagram showing configurations of receivers used inexamples of the present invention;

FIG. 32 are graphs showing measurement results of examples of thepresent invention; and

FIG. 33 is a view schematically showing a configuration of an embodimentof an inspection apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, referring to the drawings, embodiments of the presentinvention will be described below.

Embodiment 1

An embodiment of an inspection method according to the present inventionwill be described step by step with reference to FIG. 1.

In this embodiment, as shown in FIG. 2, assuming that the segment from amanhole 2 to a manhole 3 is one block, tests, measurements and the like,which will be described later, are carried out on each of the reinforcedconcrete pipe 1 (Hume pipe) constituting the one block.

[Washing Step S0]

When a large amount of extraneous matter remains on the inner surface ofthe pipe to be inspected, defects are prevented from being detected. Theextraneous matter is to be removed by means of cutting using a cuttingmachine or a water jet washing.

[Inspection Step S1]

The following appearance test and impact elastic wave test are carriedout.

<Appearance Test>

Corrosion abrasion, cracks, breakage, leakage of water or the like,which are recognizable on the inner surface of the pipe, are checked. Asfor the inspection method, when the diameter of the pipe to be inspectedis large enough, an inspector carries out the inspection by the nakedeye. When the diameter is too small for the inspector person (criterion:φ 800 mm), a TV camera is placed into the pipe to carry out theinspection.

<Impact Elastic Wave Test>

Hammering is carried out on the inner surface at an end portion of thepipe to be inspected using a hammer, a steel ball or an impulse hammer.Propagated waves are detected with an acceleration sensor or amicrophone placed on the inner surface at the other end portion of thepipe to be inspected. Speed, decay time, magnitude, resonant frequency,phase and the like of the propagated waves are calculated and comparedwith a perfectly sound item to check for existing deterioration.

To detect the level of deterioration, a simple method, in which thelevel of deterioration is detected based on changes in the resonantfrequency or changes in decay time, is available. That is, when thedeterioration progresses, since the resonant frequency and the decaytime decrease, the deterioration level can be readily detected in aquantitative manner.

In the impact elastic wave test, it is preferred to apply the hammeringwith the same force on a constant basis. For example, a method, in whicha steel ball or the like is released using a Schmitt hammer or a spring;or, a method, in which a steel ball or the like is dropped from aspecific height, is employed. Further, a method, in which hammeringforce of an impulse hammer is measured beforehand in order to take intoconsideration the influence of the hammering force at data analysis, maybe employed.

In the inspection in step S1, the impact elastic wave test may becarried out only in an area other than the area where it can bedetermined as obviously being deteriorated by the appearance test. Inorder to correctly classify the progression level of the deterioration,both tests of the appearance test by visual check (TV camera) and theimpact elastic wave test may be carried out in the entire area. That is,by carrying out the impact elastic wave test, based on the test result,the progression level of deterioration in the component segmentconstituting area to be inspected can be classified.

In the inspection in step S1, when it is determined that the inspectedpipe is difficult to be used, the following steps S2 to S7 may beomitted. And the reinforced concrete pipe may be replaced with a new oneimmediately.

[Inspection Portion Selecting Step S2]

Portion to be inspected in detail is selected based on the inspectionresult of the inspection in step S1.

The criterion of the selection from the following criteria may beemployed; i.e., (1) a portion where the deterioration has mostprogressed; (2) a portion where the progress level of the deteriorationis intermediate; (3) a portion where no deterioration is found; and (4)a combination of (1) and (2) above. However, from the point of view ofpreventing an accident from occurring during actual use, it is preferredto select “a portion where the deterioration has most progressed.”

[Measuring Step S3]

Measurement of pipe thickness to be inspected, determination ofdeteriorated portion (position of cracks) and measurement of depth ofcracks are carried out. In any measurements, elastic waves of 20 kHz to1 MHz are injected from an injecting device into the pipe to beinspected, and the propagated waves are detected and measured by areceiving unit. When the frequency of the elastic wave is 20 kHz orless, quantitative measurement is impossible; and when it is higher than1 MHz, a large diffusion results and the analysis is difficult.

As for the injecting device, a transmitter (vibrator) employing apiezoelectric element is preferably used. Also, as for the receivingunit, a receiver employing a piezoelectric element is preferably used.

Each item for measurement will be described.

<Measurement of Pipe Thickness>

Based on the propagation time from a point in time when elastic wavesare injected into the wall of the pipe from the inside of the pipe to beinspected up to a point in time when the elastic waves, which arereflected at the outer surface of the pipe, are detected by thereceiving unit, the pipe thickness is measured. For measurement ofthickness of pipe, for convenience of measurement, atransmitting/receiving sensor, in which a transmitter and a receiver areintegrated, is preferably used.

<Determination of Deteriorated Portion>

Receivers are disposed at a plurality of points on the pipe to beinspected, and the propagation time from the transmitter to eachreceiver is measured to determine deteriorated portions.

<Measurement of Crack Depth>

The depth of cracks in the determined deteriorated portion is measuredusing, for example, a method set forth in “Concrete DiagnosisTechnique 1) 1 [Basic] 4.4.2 (5) (a) (c);” or a technique disclosed inJapanese Published Examined Patent Application No. H6-52259.

It is not always necessary to carry out the above measurement of pipethickness, determination of the deteriorated portion and measurement ofthe depth of cracks. Depending on the deterioration state, the items maybe appropriately selected.

For example, when it is apparent that the deterioration is abrasiononly, only the measurement of pipe thickness is carried out. When thedeterioration is a crack only, only the determination of thedeteriorated portion and the measurement of the depth of a crack iscarried out.

[Reinforcing Bar Disposition Checking Step S4]

The disposition of reinforcing bars is checked using an electromagneticinduction type inspection machine or an electromagnetic wave typeinspection machine, which are generally available from the market. Asinspection machines of this type, an X-ray type is also available.However, in the case of the X-ray type, since the pipe wall has to betransmitted, it is difficult to apply the X-ray type inspection machineto the existing concrete pipes.

When the disposition of the reinforcing bars is recorded in drawings orthe like, the disposition of reinforcing bars in the drawings may beused as the data, and the checking step of the disposition ofreinforcing bars using an inspection machine may be omitted accordingly.

[Concrete Solid-State Properties Measuring Step S5]

Strength of concrete is measured by means of a compressive strength testusing a common core sampling, a needle insertion test (JapanesePublished Unexamined Patent Application No. H10-090150) using a smalldiameter core or a strength test using a Schmitt hammer and the like.

When the strength of concrete is measured by means of core sampling, theprogression level of neutralization of the reinforcing bars may bemeasured using an indicator such as phenolphthalein.

[Reinforcing Bar Diameter Measuring Step S6]

Core sampling is carried out, and when a reinforcing bar is included,the diameter of the reinforcing bar is measured directly.

Further, as another method, the following method may be employed. Thatis, a part of the concrete is broken off. Using a self-potential methodfor detecting the corrosion level of the reinforcing bar based on thepotential difference between the exposed reinforcing bar and the surfaceof the concrete, the relationship between the reinforcing bar corrosionlevel and the diameter of the reinforcing bar is calculated beforehand.The diameter of the reinforcing bar is calculated based on the corrosionlevel of an object. When breaking off, using an indicator such asphenolphthalein, the progression level of neutralization of thereinforcing bar may be measured.

Here, in the above described measuring step S3, when the reinforcingbars are surveyed by means of electromagnetic induction, since thediameter of the reinforcing bars can be measured at the same time, thediameter reinforcing bar measuring step S6 may be omitted.

Depending on the workability, the order of the above steps S3 to S6 maybe changed.

[Calculating Step S7]

Using the data obtained in the above-described steps, structuralanalysis is carried out to calculate the strength of a pipe (breakingload) of the reinforced concrete pipe.

The technique of structural analysis will be described in particular.

First, in a model M (¼ model) as shown in FIG. 3, configuration data asshown in FIG. 4 (A: nominal diameter, B: thickness of pipe, C: diameterof the reinforcing bar (straight reinforcing bar), D: pitch ofreinforcing bar, E: cage diameter of reinforcing bar, F: depth toreinforcing bar, G: length of pipe) are given. Then, load W is appliedto the center on the top of the model M. The stress in the load applyingprocess is calculated by means calculation.

Using a stress value obtained by the calculation and the load, aload-stress curve as shown in FIG. 5 is created. In the createdload-stress curve, reading the breaking criterion of the concrete as 4.9MPa (0.5 kg/mm²), the breaking load was obtained.

The above-described structural analysis is carried out on the pipe to beinspected (reinforced concrete pipe) to obtain the breaking load. In thedata used for structural analysis, for the thickness of pipe (B), thedata, which are measured in measuring step S3, are used; and for thediameter of the reinforcing bar (straight reinforcing bar) (C), thedata, which are measured in diameter reinforcing bar measuring step S6,are used. Also, for the pitch of reinforcing bar (D), the cage diameterof reinforcing bar (E) and the depth to reinforcing bar (F), the data,which are calculated based on the disposition of the reinforcing barschecked in reinforcing bar disposition checking step S4, are used.

Using the breaking load of the pipe to be inspected, which was obtainedby the above-described structural analysis and calculation, and byobtaining the scale of the breaking load with respect to the designedload, the deterioration state of the pipe to be inspected can beevaluated in a quantitative manner.

In this embodiment, in the inspection step S1, the classification of thedeterioration level is evaluated in a quantitative manner. Accordingly,based on the strength of the pipe in a portion to be inspected indetail, the strength of the pipe in each of the component segments canbe can be estimated.

Structural calculation software for carrying out the above-describedstructural analysis is available on the market. It is preferable to usesoftware to carry out the above steps efficiently.

In addition to the above-described evaluation using the breaking load,using the measurement data of the position of cracks, depth of thecracks and strength of the concrete, the deterioration state of the pipeto be inspected may be determined comprehensively.

EXAMPLE 1

A specific example of the present invention will be described.

[Preparation of Sample]

The following samples of a product (inside diameter 400 mm) manufacturedby Nippon Hume Corporation conforming to JIS A5303 Type A-2 wasprepared.

Sample T11: perfectly sound product

Sample T12: item introduced with water leak crack (deteriorationprogress level maximum)

Sample T13: item of which a part (central area) of bottom portion in thepipe inner surface was corroded with 1% vitriolic acid by approximately1 mm in thickness (refer to FIG. 6)

[Measuring Device]

Hammer: Schmitt hammer NR (manufactured by Fuji Bussan Co., Ltd.)

Receiver: AS-5 GB (manufactured by KYOWA Instruments Co., Ltd.)

Recording unit: EDX1500A (with amplifier) (manufactured by KYOWAInstruments Co., Ltd.)

[Disposition of Measuring Device]

Disposition shown in FIG. 7 was employed.

[Analysis Resonant Frequency]

The data of the propagated elastic wave, which were measured using thedisposition of the measuring devices shown in FIG. 7, were processedinto a power spectrum of the resonant frequency using an FFT functionprovided for the recording unit to obtain the top peak. The results areshown in Table 1.

By carrying out the above process, classification of the deteriorationof the reinforced concrete pipe can be determined quantitatively.

Embodiment 2

An other embodiment of the present invention will be described.

An injecting device and receiver used in the impact elastic wave testwill be described first.

As for the injecting device, a hammering tool such as a hammer, a steelball or an impulse hammer is available. In the impact elastic wave test,since it is preferred to carry out the hammering with the same force ona constant basis, for example, a method, in which the steel ball or thelike is released with a specific force using a Schmitt hammer or spring;or a method, in which the steel ball or the like is dropped from aspecific height, is employed. Further, a method, in which the hammeringforce of the impulse hammer is measured beforehand to take the influenceof the hammering force into consideration during the data analysis, maybe employed.

As for the receiver, an acceleration sensor, an AE sensor and vibrationsensor or the like is available.

As for the setting method of the receiver, the receiver may be fixedusing an adhesive tape or agent, or may be brought into contact with theobject by hand, a holding tool or the like.

The injecting device and receiver may come into contact with water, acidwater or basic water. Accordingly, the injecting device and receiver arepreferably constituted with a material such as SUS, which is superior inanti-corrosion.

Next, the measuring method and analyzing method of the received waveswill be described.

[Measuring Method]

An impact is given to the inner surface at an end portion of a pipe tobe inspected using the injecting device, the propagated waves aredetected by the receiver, which is set on the inner surface at other endportion of the pipe to be inspected, and the waveform data is stored inthe recording unit. In the measurement described above, it is preferredthat the distance between the elastic wave injecting position by theinjecting device and the elastic wave receiving position by the receiveris ¼ or more of the length of the pipe to be inspected away from eachother. By prescribing the distance between the elastic wave injectingposition and the elastic wave receiving position as described above, thechanges in vibration mode of the entire pipe due to deterioration causedfrom cracks can be detected easily.

[Analyzing Method of the Received Waves]

First, FFT analysis is made on the waveform data stored in the recordingunit, and a resonant frequency spectrum chart is created (refer to FIG.11). Then, integration processing is made on the created resonantfrequency spectrum chart, and a high frequency component and lowfrequency component are obtained. And thus, the area ratio between thearea of the high frequency component and the area of the low frequencycomponent is calculated. In particular, with respect to the resonantfrequency spectrum, by dividing with 4 kHz as the boundary, area ratiosbetween the range of 0 to 4 kHz and the range of 4 to 8 kHz areobtained, and the deterioration level of the pipe to be inspected isdetermined based on the area ratio.

In the above analysis, the boundary value (for example 4 kHz) betweenthe high frequency and the low frequency may be preset. It is preferredto make a determination at the measuring site depending on the type ofthe pipe to be inspected for facilitating the determination.

EXAMPLE 2

A specific example of the present invention will be described.

[Sample Preparation]

The following samples were prepared using a product (inside diameter 250mm) manufactured by Nippon Hume Corporation, conforming to JIS A 5303type B, which were cut off as shown in FIG. 8

-   -   Sample T21: Unprocessed product    -   Sample T22: item introduced with axial cracks    -   Dropped on concrete surface to generate four cracks in the axial        direction    -   Sample T23: item introduced with axial cracks

Dropped on concrete surface to generate ten cracks in the axialdirection (refer to FIG. 10). As for the number of the cracks in thesamples T22 and T23, the number of cracks generated on the inner andouter surfaces was checked at one end surface by visual check.

-   -   Sample T24: item of which inner surface was ground.

The reinforcing bars were exposed out of the inner surface layer bymeans of water jet blasting. Amount of grinding was set so as to be 1.6mm in average grinding thickness. The ground amount was measured at tenpoints on each end in an area adjacent to the pipe end; total 20 points,using a slide caliper.

List of samples is shown in Table 2.

[Injection and Receiving Position]

The injecting device and the receiving unit are disposed at thepositions shown in FIG. 9, and injection of elastic waves and receptionof propagation waves were performed.

[Used Apparatus]

Injecting device: P type Schmitt hammer

Receiver: a cylindrical item of a diameter of 10 mm and height of 15 mm,was attached onto a male screw on a vibration sensor GH-313A(manufactured by Keyence Corporation). The receiver was set and held byhand.

Receiving amplifier: GA-245 (manufactured by Keyence Corporation)

Data logger (recording unit): NR-350 (manufactured by KeyenceCorporation)

[Data Analysis]

Using the waveform data of the propagation waves received and recordedwith the above apparatus, power spectrum of the resonant frequency wascreated by using the FFT analyzing program (manufactured by APTEC).Resonant frequency spectrums of the respective samples are shown inFIGS. 11 (a) to (d).

Then, with respect to each of the resonant frequency spectrums in FIGS.11( a) to (d), by dividing with 4 kHz as the boundary, area ratiosbetween the range of 0 to 4 kHz and the range of 4 to 8 kHz are obtainedby Igor Pro (manufactured by Wave Metrics). The results are shown inTable 3 and FIG. 12.

As demonstrated in Table 3 and FIG. 12, it is understood that, when theprogression level of the deterioration becomes large, the ratio of thelow frequency component becomes higher. Accordingly, based on the arearatio between the high frequency component and the low frequencycomponent in the resonant frequency spectrum of the propagation waves,the deterioration level of the pipe to be inspected can be determinedquantitatively.

Embodiment 3

An other embodiment of the present invention will be described.

First, the injecting device and receiver used for the impact elasticwave test will be described.

As for the injecting device, a hammering tool such as a hammer, a steelball or an impulse hammer is available. In the impact elastic wave test,since it is preferred to carry out the hammering with the same force ona constant basis, for example, a method, in which the steel ball or thelike is released with a specific force using a Schmitt hammer or spring,or a method, in which the steel ball or the like is dropped from aspecific height, is employed. Further, a method, in which the hammeringforce of the impulse hammer is measured beforehand to take the influenceof the hammering force into consideration during the data analysis, maybe employed.

As for the receiver, an acceleration sensor, an AE sensor and vibrationsensor or the like is available.

As for the setting method of the receiver, the receiver may be fixedusing an adhesive tape or agent, or may be brought into contact with theobject by hand, a holding tool or the like.

The injecting device and receiver may come into contact with water, acidwater or basic water. Accordingly, the injecting device and receiver arepreferably constituted of a material such as SUS, which is superior inanti-corrosion.

Next, the measuring method and analyzing method of the received waveswill be described.

[Measuring Method]

An impact is given to the inner surface at the end portion of a pipe tobe inspected using the injecting device, the propagated waves aredetected by the receiver set on the inner surface at the other endportion of the pipe to be inspected, and the waveform data is stored inthe recording unit. In the measurement described above, it is preferredthat the distance between the elastic wave injecting position by theinjecting device and the elastic wave receiving position by the receiveris ¼ or more of the length of the pipe to be inspected away from eachother. By prescribing the distance between the elastic wave injectingposition and the elastic wave receiving position as described above, thechanges in vibration mode of the entire pipe due to deterioration causedfrom cracks can be detected easily.

[Analyzing Method of Received Wave]

First, FFT analysis is made on the waveform data stored in the recordingunit, and a resonant frequency spectrum chart is created (refer to FIG.15). Then, the strength ratio between the top peak strength in thefrequency range of 4 to 10 kHz (high frequency range) and the top peakstrength in the frequency range of 3 to 4 kHz (low frequency range) ofthe created resonant frequency spectrum is calculated. And based on thecalculated top peak strength ratio, the deterioration level of the pipeto be inspected is determined.

In this embodiment, a phenomenon, in which, as the deterioration of thereinforced concrete pipe proceeds, the vibration mode changes, and thevibration constituting the resonant frequency also changes, is utilized.

EXAMPLE 3

A specific example of the present invention will be described.

[Sample Preparation]

The following samples were prepared using a product (inside diameter 250mm) manufactured by Nippon Hume Corporation, conforming to JIS A 5303type B, which were cut off as shown in FIG. 8

-   -   Sample T31: Non-processed    -   Sample T32: Item introduced with peripheral cracks

Item, which is introduced with a crack of 0.15 mm in width by means ofintroduction as shown in FIG. 13 (refer to FIG. 14).

-   -   Sample T33: Item introduced with peripheral cracks

Item, which is introduced with a crack of 1.3 mm in width by means ofintroduction as shown in FIG. 13 (refer to FIG. 14). The width of cracksin the samples T32 and T33 were measured while being enlarged by amagnifier with a scale (average of values at 5 points).

List of samples is shown in Table 4.

[Injection and Receiving Position]

The injecting device and the receiving unit were disposed at theposition shown in FIG. 9, and the injection of elastic waves andreception of the propagated waves were carried out.

[Used Apparatus]

Injecting device: P type Schmitt hammer

Receiver: a cylindrical item of a diameter of 10 mm, a height of 15 mm,was attached onto a male screw on a vibration sensor GH-313A(manufactured by Keyence Corporation). The receiver was set and held byhand.

Receiving amplifier: GA-245 (manufactured by Keyence Corporation)

Data logger (recording unit): NR-350 (manufactured by KeyenceCorporation)

[Data Analysis]

Using the waveform data of the propagation waves received and recordedwith the above apparatus, power spectrum of the resonant frequency wascreated by using the FFT analyzing program (manufactured by APTEC).Resonant frequency spectrums of the respective samples are shown in FIG.15 (a) to (c).

Then, with respect to each of the resonant frequency spectrums in FIGS.15( a) to (c), the top peak strength in the frequency range (highfrequency range) of 4 to 10 kHz and the top peak strength in thefrequency range (low frequency range) of 3 to 4 kHz were calculated. Andthe strength ratio between the top peak strength in the frequency rangeof 4 to 10 kHz and the top peak strength in the frequency range of 3 to4 kHz was calculated. The results are in Table 5.

As demonstrated in Table 5, when the progression level of deteriorationof the pipe to be inspected becomes larger, the ratio (P1/P2) of the toppeak strength (P1) in the frequency range of 4 to 10 kHz with respect tothe top peak strength (P2) in the frequency range in 3 to 4 kHz becomeslarger. Accordingly, by obtaining the ratio between the top peakstrength in the frequency range of 4 to 10 kHz and the top peak strengthin the frequency range of 3 to 4 kHz in the resonant frequency spectrumof the propagation waves, based on the strength ratio, the deteriorationlevel of the pipe to be inspected can be determined quantitatively.

Embodiment 4

Still another embodiment of the present invention will be described.

Injecting device and receiver used in the impact elastic wave test willbe described first.

As for the injecting device, a hammering tool such as a hammer, a steelball or an impulse hammer is available. In the impact elastic wave test,since it is preferred to carry out the hammering with the same force ona constant basis, for example, a method, in which the steel ball or thelike is released with a specific force using a Schmitt hammer or aspring, or a method, in which the steel ball or the like is dropped froma specific height is employed. Further, a method, in which hammeringforce of the impulse hammer is measured beforehand to take the influenceof the hammering force into consideration during the data analysis, maybe employed.

As for the receiver, an acceleration sensor, an AE sensor and vibrationsensor or the like is available.

As for the setting method of the receiver, the receiver may be fixedusing an adhesive tape or agent, or may be brought into contact with theobject by hand, a holding tool or the like.

The injecting device and receiver may come into contact with water, acidwater or basic water. Accordingly, the injecting device and receiver arepreferably constituted of a material such as SUS, which is superior inanti-corrosion.

Next, the measuring method and analyzing method of the received waveswill be described.

[Measuring Method]

An impact is given to the inner surface at the end portion of a pipe tobe inspected using the injecting device, the propagated waves aredetected by the receiver set on the inner surface at the other endportion of the pipe to be inspected, and the waveform data is stored inthe recording unit. In the measurement described above, it is preferredthat the distance between the elastic wave injecting position by theinjecting device and the elastic wave receiving position by the receiveris ¼ or more of the length of the pipe to be inspected away from eachother. By prescribing the distance between the elastic wave injectingposition and the elastic wave receiving position as described above, thechanges in vibration mode of the entire pipe due to deterioration causedfrom cracks can be detected easily.

[Analyzing Method of the Received Waves]

First, the maximum amplitude value in the propagation waves stored inthe recording unit was obtained, based on maximum magnitude value, thedeterioration level of the entire pipe to be inspected is determined.The “maximum amplitude value of the propagation wave” is defined as amaximum amplitude value at which the absolute value is the maximum inthe waveform data of the propagation waves as shown in FIG. 16.

EXAMPLE 4

A specific example of the present invention will be described.

[Sample Preparation]

The following samples were prepared using a product (inside diameter 250mm) manufactured by Nippon Hume Corporation, conforming to JIS A 5303type B, which were cut off as shown in FIG. 8.

Sample T41: non-processed item

Sample T42: item introduced with axial cracks

Item dropped on a concrete surface and generated with four cracks in theaxial direction.

Sample T43: item introduced with axial cracks

Item dropped on concrete surface and generated with ten cracks in theaxial direction (refer to FIG. 10). The number of the cracks in thesamples T42 and T43, which were generated on the inner and outersurface, was visually checked at one end surface thereof.

-   -   Sample T44: item introduced with peripheral cracks

Item generated with cracks with width of 0.15 mm in the peripheraldirection by means of crack introducing method shown in FIG. 13 (referto FIG. 14).

-   -   Sample T45: item introduced with peripheral cracks

Item generated with cracks with width of 1.3 mm in the peripheraldirection by means of crack introducing method shown in FIG. 13 (referto FIG. 14). The width of cracks in the samples T44 and T45 weremeasured while being enlarged by a magnifier with a scale (average ofvalues at 5 points).

The list of samples is shown in Table 6.

[Injection and Receiving Position]

The injecting device and the receiving unit are disposed at positionsshown in FIG. 9, injection of elastic waves and reception of propagationwaves were carried out.

[Used Apparatus]

Injecting device: P type Schmitt hammer

Receiver: a cylindrical item of a diameter of 10 mm, a height of 15 mm,was attached onto a male screw on a vibration sensor GH-313A(manufactured by Keyence Corporation). The receiver was set and held byhand.

Receiving amplifier: GA-245 (manufactured by Keyence Corporation)

Data logger (recording unit): NR-350 (manufactured by KeyenceCorporation)

[Data Analysis]

Using the waveform data of the propagation waves received and recordedwith the above apparatus, maximum amplitude values (refer to FIG. 16) ofthe samples were obtained. The results are shown in Table 7.

As demonstrated in Table 7, when the deterioration progression level ofthe pipe to be inspected becomes larger, the maximum amplitude value ofthe propagation waves becomes smaller. Accordingly, by obtaining themaximum amplitude value of the propagation waves from the waveform data,based on the maximum amplitude value, the deterioration level of thepipe to be inspected can be determined quantitatively.

Embodiment 5

In this embodiment, from the data indicating the deteriorationphenomena; i.e., (1) the area ratio between the high frequency componentand the low frequency component in a resonant frequency spectrum of thepropagation waves; (2) the ratio of the top peak strength between thefrequency range of 4 to 10 kHz and the frequency range of 3 to 4 kHz ina resonant frequency spectrum of the propagation waves; (3) maximumamplitude value of the propagation waves; and (4) a combination of dataof the decay time of the propagation waves, the classification ofdeterioration phenomenon and deterioration progression level can bedetermined based on Table 8.

Here, the wording “decay time of propagation waves” means a period oftime when the amplitude value of the propagation waves (received waves)becomes a certain value or less as shown in FIG. 17. In particular, forexample, when vibrations, in which the absolute value of the amplitudevalue is 20% or less with respect to the absolute value of the maximumamplitude value, continue for three times or more, it is defined thatthe waves up to the first point are “input waves;” and the period oftime up to the first point is “decay time.”

Next, referring to the flowcharts shown in FIG. 18 to FIG. 22, anexample of a particular determination processing will be described.

[Determination Processing J1: FIG. 18]

Step S101: Analysis of changes in the decay time of the propagationwaves. When no change is found in the decay time, the process proceedsto step S102. When a change is found in the decay time, the processproceeds to step S111. The analysis of the change in the decay time ismade by comparison with a perfectly sound item.

Step S102: When no change is found in the decay time of the propagationwaves, the item is recognized as “no deterioration,” or, either or bothof “item with peripheral crack” and/or “item with reduced pipethickness” are possible (refer to Table 8).

Step S103: Analysis of the maximum amplitude value of the propagationwaves. When no change is found in the maximum amplitude value, theprocess proceeds to step S104. When a change is found in the maximumamplitude value, the process proceeds to step S131. The analysis of thechanges of maximum amplitude value is made by comparison with aperfectly sound item.

Step S104: When no change is found in the decay time or the maximumamplitude value of the propagation waves, the item is recognized as “nodeterioration” or “item with reduced pipe thickness” (refer to Table 8).

Step S105: Resonant frequency spectrum chart (refer to FIG. 11) iscreated using the FFT.

Step S106: Analysis of the area ratio between the low frequency rangeand the high frequency range in the resonant frequency spectrum (for adetailed analysis process, refer to the above-described Embodiment 2).When a change is found in the area ratio, (increase of low frequencycomponent), the item is determined as “item with reduced pipe thickness”(step S107). Based on the area ratio, the deterioration level isdetermined (step S108). On the other hand, when no change is found inthe area ratio, the item is determined as “no deterioration” (stepS109).

Step S111: In the analysis in step S101, when a change is found in decaytime (reduction), the item is recognized as “item generated with axialcrack.” When the pipe to be inspected is recognized as “item generatedwith axial crack,” determination process of the deterioration level iscarried out by means of maximum magnitude value analysis (step S112).Or, a resonant frequency spectrum chart (refer to FIG. 11) is createdusing the process in steps S121 and S122; i.e., FFT. Then, the arearatio between the low frequency range and the high frequency range ofthe resonant frequency spectrum was obtained. Based on the area ratio,processing to determine the deterioration level is carried out.

Step S131: When a change is found in the amplitude value (reduction) inthe analysis in step S103, the item is recognized as “item generatedwith peripheral crack.” When the pipe to be inspected is recognized as“item generated with peripheral crack,” the deterioration level isdetermined by means of maximum magnitude value analysis (step S132). Or,a resonant frequency spectrum chart (refer to FIG. 15) is created usingthe process in steps S141 and S142; i.e., FFT. Then, the top peakstrength ratio between the frequency range of 4 to 10 kHz and thefrequency range of 3 to 4 kHz in the resonant frequency spectrum of thepropagation waves is analyzed (for a detailed analysis process, refer toEmbodiment 3). Based on the strength ratio, the deterioration level isdetermined.

[Determination Processing J2: FIG. 19]

Step S201: Analysis of the changes in the decay time of the propagationwaves. When no change is found in the decay time, the process proceedsto step S202. When a change is found in the decay time, the processproceeds to step S211. The analysis of changes in the decay time is madeby comparison with a perfectly sound item.

Step S202: When no change is found in the decay time of the propagationwaves, the item is recognized as “no deterioration,” or either or bothof “item generated with peripheral crack” and/or “item with reduced pipethickness” (refer to Table 8).

Step S203: Resonant frequency spectrum chart is created using the FFT(refer to FIG. 11).

Step S204: Analysis of the area ratio between the low frequency rangeand the high frequency range in the resonant frequency spectrum (for adetailed analysis process, refer to Embodiment 2). When a change isfound in the area ratio (increase of low frequency component), the itemis determined as “item with reduced pipe thickness” (step S205). Then,based on the area ratio, the deterioration level is determined (stepS206). On the other hand, when no change is found in the area ratio, theprocess proceeds to step S231.

Step S211: In the analysis in step S201, when a change is found in thedecay time (reduction), the item is recognized as “item generated withaxial crack.” When the pipe to be inspected is recognized as “itemgenerated with axial crack,” the deterioration level is determined bymeans of maximum magnitude value analysis (step S212). Or, a resonantfrequency spectrum chart (refer to FIG. 11) is created using theprocessing of steps S213 and S214; i.e., FFT. Then, the area ratiobetween the low frequency range and the high frequency range in theresonant frequency spectrum is analyzed. Based on the area ratio,processing to determine the deterioration level is carried out.

Step S231: In the analysis in step S204, when no change is found in thearea ratio, the item is recognized as “no deterioration” or “itemgenerated with peripheral crack” (refer to Table 8).

Step S232: The maximum amplitude value in the propagation waves isanalyzed, and when no change is found in the maximum amplitude value,the item is recognized as “no deterioration.” On the other hand, when achange is found in the maximum amplitude value (reduction in amplitude),the item is recognized as “item generated with peripheral crack” (stepS233). When the pipe to be inspected is recognized as “item generatedwith peripheral crack,” processing to determine the deterioration levelis carried out (step S234) by means of maximum magnitude value analysis.Or, processing steps from S241 to S244 are carried out. The analysis ofchanges in the maximum amplitude value is made by comparison with aperfectly sound item.

In the processing of the steps from S241 to S244, the resonant frequencyspectrum chart (refer to FIG. 15) is created using the FFT. The top peakstrength ratio between the frequency range of 4 to 10 kHz and thefrequency range of 3 to 4 kHz in the resonant frequency spectrum isanalyzed (for a detailed analysis process, refer to the above-describedEmbodiment 3). In this analysis, when a change is found in the top peakstrength ratio (ratio increase), the item is recognized as “itemgenerated with peripheral crack.” Then, based on the strength ratio, thedeterioration level is determined. When no change is found in the toppeak strength ratio in the analysis in step S242, the item is determinedas “no deterioration.”

[Determination Processing J3: FIG. 20]

Step S301: Analysis of the maximum amplitude value of the propagationwaves. When a change (reduction in amplitude) is found in the maximumamplitude value, the process proceeds to step S302. When no change isfound in the maximum amplitude value, the process proceeds to step S321.The analysis of changes in the maximum amplitude value is made bycomparison with a perfectly sound item.

Step S302: When a change is found in the maximum amplitude value of thepropagation waves, the item is recognized as either or both of “itemgenerated with axial crack” and/or “item generated with peripheralcrack” (refer to Table 8).

Step S303: Analysis of changes in the decay time of the propagationwaves. When a change is found in the decay time (reduction in decaytime), the process proceeds to step S331. The analysis of changes in thedecay time is made by comparison with a perfectly sound item.

On the other hand, when no change is found in the decay time, the itemis recognized as “item generated with peripheral crack” (step S304).When the pipe to be inspected is recognized as “item generated withperipheral crack,” the deterioration level is determined by means ofmaximum magnitude value analysis (step S305). Or, a resonant frequencyspectrum chart (refer to FIG. 15) is created using the process in stepsS315 and S316; i.e., FFT. Then, the top peak strength ratio between thefrequency range of 4 to 10 kHz and the frequency range of 3 to 4 kHz inthe resonant frequency spectrum of the propagation waves is analyzed(for a detailed analysis process, refer to the above Embodiment 3).Based on the strength ratio, a processing to determine the deteriorationlevel is carried out.

Step S321: In the analysis in step S301, when no change is found in theamplitude value, the item is recognized as “no deterioration” or “itemwith reduced pipe thickness” (refer to Table 8).

Step S322: A resonant frequency spectrum chart is created using the FFT(refer to FIG. 11).

Step S323: The area ratio between the low frequency range and the highfrequency range in the resonant frequency spectrum is analyzed (for adetailed analysis process, refer to the above Embodiment 2). When achange (increase of low frequency component) is found in the area ratio,the item is determined as “item with reduced pipe thickness” (stepS324). Then, based on the area ratio, the deterioration level isdetermined (step S325). On the other hand, when no change is found inthe area ratio, the item is determined as “no deterioration” (stepS326).

Step S331: In the analysis in step S303, when a change is found in thedecay time (reduction), the item is recognized as “item generated withaxial crack.” When the pipe to be inspected is recognized as “itemgenerated with axial crack,” the deterioration level is determined bymeans of maximum magnitude value analysis (step S332). Or, a resonantfrequency spectrum chart (refer to FIG. 11) is created using theprocessing in steps S341 and S342; i.e., FFT. Then, the area ratiobetween the low frequency range and the high frequency range in theresonant frequency spectrum is calculated. Based on the area ratio,processing to determine the deterioration level is carried out.

[Determination Processing J4: FIG. 21]

Step S401: Analysis of the maximum amplitude value in the propagationwaves. When a change (reduction in amplitude) is found in the maximumamplitude value, the process proceeds to step S402. When no change isfound in the maximum amplitude value, the process proceeds to step S411.The analysis of changes in the maximum amplitude value is made bycomparison with a perfectly sound item.

Step S402: When a change is found in the maximum amplitude value of thepropagation waves, the deterioration level is classified based on thereduced amount of the maximum amplitude value. When a change is found inthe decay time and the maximum amplitude value of the propagation waves,the item is recognized as either or both of “item generated with axialcrack” and “item generated with peripheral crack” (refer to Table 8).

Step S403: A resonant frequency spectrum chart (refer to FIG. 11) iscreated using FFT.

Step S404: The area ratio between the low frequency range and the highfrequency range in the resonant frequency spectrum is analyzed (foranalysis process, refer to the above Embodiment 2). When a change(increase of low frequency component) is found in the area ratio, theitem is determined as “item generated with axial crack” (step S405). Onthe other hand, when no change is found in the area ratio, the item isdetermined as “item generated with peripheral crack” (step S406).

Step S411: In the analysis in step S401, when no change is found in theamplitude value, the item is recognized as “no deterioration” or “itemwith reduced pipe thickness” (refer to Table 8).

Step S412: A resonant frequency spectrum chart (refer to FIG. 11) iscreated using the FFT.

Step S413: The area ratio between the low frequency range and the highfrequency range in the resonant frequency spectrum is analyzed (for adetailed analysis process, refer to Embodiment 2). When a change(increase of low frequency component) is found in the area ratio, theitem is determined as “item with reduced pipe thickness” (step S414).Then, based on the area ratio, the deterioration level is determined(step S415). On the other hand, when no change is found in the arearatio, the item is determined as “no deterioration” (step S416).

[Determination Processing J5: FIG. 22]

Step S501: Analysis of the maximum amplitude value in the propagationwaves. When a change (reduction in amplitude) is found in the maximumamplitude value, the process proceeds to step S502. When no change isfound in the maximum amplitude value, the process proceeds to step S511.The analysis of the change in maximum amplitude value is made bycomparison with a perfectly sound item.

Step S502: When a change is found in the maximum amplitude value of thepropagation waves, the deterioration level is classified based on thereduced amount of the maximum amplitude value. When a change is found inthe decay time and the maximum amplitude value of the propagation waves,the item is recognized as either or both of “item generated with axialcrack” or “item generated with peripheral crack” (refer to Table 8).

Step S503: Analysis of change in the decay time of the propagationwaves. When a change (reduction in the decay time) is found in the decaytime, the item is determined as “item generated with axial crack” (stepS504). On the other hand, when no change is found in the decay time, theitem is determined as “item generated with peripheral crack” (stepS505).

Step S511: In the analysis in step S501, when no change is found in theamplitude value, the item is recognized as either or both of “nodeterioration” or “item with reduced pipe thickness” (refer to Table 8).

Step S512: A resonant frequency spectrum chart (refer to FIG. 11) iscreated using the FFT.

Step S513: Analysis of area ratio between the low frequency range andthe high frequency range in the resonant frequency spectrum (foranalysis processing, refer to the above Embodiment 2). When a change(increase of low frequency component) is found in the area ratio, theitem is determined as “item with reduced pipe thickness” (step S514).Then, the deterioration level is determined based on the area ratio(step S515). On the other hand, when no change is found in the arearatio, the item is determined as “no deterioration” (step S516).

EXAMPLE 5

A specific example of the present invention will be described.

[Sample Preparation]

The following samples were prepared using a product (inside diameter 250mm) manufactured by Nippon Hume Corporation, conforming to JIS A 5303type B, which were cut off as shown in FIG. 8.

-   -   Sample T51: non-processed item    -   Sample T52: item introduced with cracks

Item dropped on a concrete surface and generated with four cracks in theaxial direction.

-   -   Sample T53: item introduced with cracks

Item dropped on concrete surface and generated with ten cracks in theaxial direction (refer to FIG. 10). The number of the cracks in thesamples T52 and T53, which were generated on the inner and outersurface, was visually checked at the one end surface thereof.

-   -   Sample T54: item introduced with peripheral cracks

Item generated with cracks with width of 0.15 mm in the peripheraldirection by means of processing of crack introducing method shown inFIG. 13 (refer to FIG. 14).

-   -   Sample T55: item introduced with peripheral cracks

Item generated with cracks with width of 1.3 mm in the peripheraldirection by means of processing of crack introducing method shown inFIG. 13 (refer to FIG. 14).

The width of cracks in the samples T54 and T55 were measured while beingenlarged by a magnifier with a scale (average of values at 5 points).

-   -   Sample T56: pipe with ground inner surface

The reinforcing bars were exposed out of the inner surface layer bymeans of water jet blasting. Amount of grinding was set so as to be 1.6mm in average grinding thickness. The ground amount was measured at tenpoints on each end in the area adjacent to the pipe end surface; total20 points, using a slide caliper.

The list of samples is shown in Table 9.

[Injection and Receiving Position]

The injecting device and the receiving unit are disposed at thepositions shown in FIG. 9, and injection of elastic waves and receptionof propagation waves were performed.

[Used Apparatus]

Injecting device: P type Schmitt hammer

Receiver: a cylindrical item of a diameter of 10 mm, a height of 15 mm,was attached onto a male screw on a vibration sensor GH-313A(manufactured by Keyence Corporation). The receiver was set and held byhand.

Receiving amplifier: GA-245 (manufactured by Keyence Corporation)

Data logger (recording unit): NR-350 (manufactured by KeyenceCorporation)

[Data Analysis]

(1) Determination of item with cracks: Based on the received waveformdata, the maximum amplitude value (refer to FIG. 16) was calculated. Theresults are in Table 10.

As demonstrated in Table 10, based on the change in the maximumamplitude value, items with cracks can be sorted from others. Also,based on the change in maximum amplitude value, the progression level ofthe cracks can be determined.

(2) Determination of Reduction in Pipe Thickness

With respect to sample T51 and sample T56, using the waveform data ofthe obtained propagation waves, the resonant frequency spectrum wasanalyzed using an FFT analyzing program (manufactured by APTEC). Then,with respect to each of the respective resonant frequency spectrums, bydividing with 4 kHz as the boundary, the area ratio between the range of0 to 4 kHz and the range of 4 to 8 kHz was obtained by Igor Pro(manufactured by Wave Metrics). The results are shown in FIG. 23.

As demonstrated in FIG. 23, it is possible to sort the item with reducedpipe thickness (sample T56) from the perfectly sound item. Based on thearea ratio, the reduction level in the pipe thickness can be determined.

(3) Sorting of Crack Type

With respect to samples T52 to T56, using the waveform data of theobtained propagation waves, the resonant frequency spectrum was analyzedusing the FFT function. Then, with respect to each of the resonantfrequency spectrums, by dividing with 4 kHz as the boundary, the arearatio between the range of 0 to 4 kHz and the range of 4 to 8 kHz wasobtained by Igor Pro (manufactured by Wave Metrics).

The results are shown in FIG. 24.

As demonstrated in FIG. 24, in the case of the peripheral crack, nochange is found in the area ratio. In the case of the axial crack,changes can be found in the area ratio. Accordingly, when a change isfound in the area ratio, it can be determined that an axial crack isgenerated, and the type of cracks can be determined.

Further based on the comparison among the samples T51 to T53, theprogress level of the axial cracks can be determined.

(4) Determination of the Progression Level of the Peripheral Cracks

With respect to the sample T54 and sample T55, using the waveform dataof the received propagation waves, resonant frequency spectrums wereobtained using the FFT function of the recording unit, and therespective resonant frequency spectrum charts were created. The resonantfrequency spectrum of each sample is shown in FIGS. 25( a) and (b).

Then, with respect to each of the resonant frequency spectrums in FIGS.25( a) and (b), top peak strength in the frequency range of 4 to 10 kHz(high frequency range) and the top peak strength in the frequency rangeof 3 to 4 kHz were obtained. And the strength ratio between the top peakstrength in the frequency range of 4 to 10 kHz and the top peak strengthof the frequency range (low frequency range) of 3 to 4 kHz wascalculated. As a result, the strength ratio in the sample T54 was 1.40;and the strength ratio in the sample T55 was 1.64. As demonstrated inthis result, based on the strength ratio between the top peak strengthin the frequency range of 4 to 10 kHz and the top peak strength in thefrequency range of 3 to 4 kHz in the resonant frequency spectrum, theprogress level of the peripheral cracks can be determined. As describedabove, using the maximum amplitude value, the progress level can bedetermined.

Embodiment 6

Still another embodiment of the present invention will be described.

The injecting device and receiver used in the impact elastic wave testwill be described first.

As for the injecting device, a hammering tool such as a hammer, a steelball or an impulse hammer is available. In the impact elastic wave test,since it is preferred to carry out the hammering with the same force ona constant basis, for example, a method, in which the steel ball or thelike is released with a specific force using a Schmitt hammer or aspring, or a method, in which the steel ball or the like is dropped froma specific height, is employed. Further, a method, in which hammeringforce of the impulse hammer is measured beforehand to take the influenceof the hammering force into consideration during the data analysis, maybe employed.

As for the receiver, an acceleration sensor, an AE sensor, vibrationsensor or the like is available.

As for the setting method of the receiver, the receiver may be fixedusing an adhesive tape or agent, or may be brought into contact with theobject by hand, a holding tool or the like.

The injecting device and receiver may come into contact with water, acidwater or basic water. Accordingly, the injecting device and receiver arepreferably constituted of a material such as SUS, which is superior inanti-corrosion.

In this embodiment, an impact elastic wave test is carried out. That is,using a hammer, a steel ball or an impulse hammer, hammering is carriedout on the inner surface at the end portion of the pipe to be inspected,propagated waves are detected with an acceleration sensor or amicrophone set on the inner surface at the other end portion of the pipeto be inspected. Speed, decay time, magnitude, resonant frequency, phaseand the like of the propagated wave are obtained. Based on thecomparison with the perfectly sound item, the existence of deteriorationis checked.

This embodiment is characterized in that, when reinforced concrete pipeconstituting a sewage conduit or irrigation conduit is inspected bymeans of the impact elastic wave test, the distance between the elasticwave injecting position and the elastic wave receiving position is setbeing away from each other by ¼ or more of the length of the pipe to beinspected.

As described above, by carrying out the impact elastic wave test in astate that the distance between the elastic wave injecting position andthe elastic wave receiving position is away from each other by ¼ or moreof the length of the pipe, changes of the vibration mode of the entirereinforced concrete pipe due to aging can be detected easily resultingin an increased accuracy of the inspection.

EXAMPLE 6

A specific example of the present invention will be described.

[Sample Preparation]

The following samples were prepared using a product (inside diameter 250mm) manufactured by Nippon Hume Corporation, conforming to JIS A 5303type B, which were cut off as shown in FIG. 8.

-   -   Sample T61: non-processed item    -   Sample T62: item introduced with axial crack

Item dropped on concrete surface and generated with ten cracks in theaxial direction (refer to FIG. 10). As for the number of cracks, numberof cracks generated on the inner and outer surfaces was visually checkedat one end surface. The number of the cracks in the samples T42 and T43,which were generated on the inner surface, was visually checked at theone end surface thereof.

[Injection and Receiving Position]

The injecting device and the receiving unit are disposed at thepositions (Example 6-1 to 6-5 and Comparison example 6-1 and 6-2) shownin FIG. 26, and injection of elastic waves and reception of propagationwaves were performed.

[Used Apparatus]

Injecting device: P type Schmitt hammer

Receiver: a cylindrical item (SUS) of a diameter of 10 mm, a height of15 mm, was attached onto a male screw on a vibration sensor GH-313A(manufactured by Keyence Corporation). The receiver was set and held byhand.

Receiving amplifier: GA-245 (manufactured by Keyence Corporation)

Data logger (recording unit): NR-350 (manufactured by KeyenceCorporation)

[Data Analysis]

Using the waveform data of the propagation waves received and recordedwith the above apparatus, maximum amplitude values (refer to FIG. 16) ofthe respective samples were obtained. The result of the above is shownin Table 11 and FIG. 27.

As demonstrated in Table 11 and FIG. 27, by setting the distance betweenthe injecting device and the receiving unit (distance between theelastic wave injecting position and the elastic wave receivingposition), ¼ or more (250 mm or more) of the length of the pipe to beinspected (1000 mm) away from each other, the generated cracks can bedetected precisely.

Embodiment 7

In the present invention, as for the receiver used for the impactelastic wave test, as shown in FIGS. 28( a) to (e), receivers 2 a-2 e,which have the front end of a cone-like or pyramid-like shape, areavailable. In the case of a receiver of which the front end is acone-like shape, as shown in FIGS. 28( f) to (i), receivers 2 f to 2 i,of which the conical surface (side surface) is formed into a curvedsurface, may be employed.

In place of a receiver having a cone-like shape as described above, areceiver of which the front end has a needle-like shape, may beemployed.

As other examples of the receivers, as shown in FIGS. 29( a) to (i),receivers 3 a to 3 i, of which the front end surface is a flat-shape,are available. In the case of a receiver of which the front end surfaceis flat as described above, the area of the front end surface is 3 cm²or less, more preferably, 2.5 cm² or less. If the area of the front-endsurface of the receiver is 3 cm² or more, the receiver fails to stablycome into contact with the inner surface of the pipe to be inspected,and accordingly, the stability of the measurement is reduced.

As still other examples of receivers, as shown in FIG. 30( a) to (g),receivers 4 a to 4 g, of which the front end surface has a curvedsurface, are available. In the case of a receiver, of which the frontend surface has a curved surface as described above, the curvatureradius of the front end surface is preferably 25 mm or less, morepreferably, 20 mm or less. If the curvature radius of the front endsurface of the receiver is 25 mm or more, the receiver fails to stablycome into contact with the inner surface of the pipe to be inspected,and accordingly, the stability of the measurement is reduced.

As for the setting method of the above-described receiver, the receivermay be fixed with an adhesive tape, agent or the like. The receiver maybe held by hand, a holding tool or the like. Also, since the receivermay come into contact with water, acid water or basic water, thereceiver is preferably made of a material such as SUS, which is superiorin anti-corrosion.

EXAMPLE 7

A specific example of the present invention will be described.

[Sample Preparation]

The following samples were prepared using a product (inside diameter 250mm) manufactured by Nippon Hume Corporation, conforming to JIS A 5303type B, which were cut off as shown in FIG. 8.

-   -   Sample with reduced pipe thickness T71: The reinforcing bars        were exposed out of the inner surface layer by means of water        jet blasting. Amount of grinding was set so as to be 1.6 mm in        average grinding thickness. The ground amount was measured at        ten points on each end surface in an area adjacent to the pipe        end; total 20 points, using a slide caliper.    -   Sample applied with lard T72: item applied with lard on the        inner surface of the pipe. Average thickness of the lard is        approximately 1 to 4 mm.

[Injection and Receiving Position]

The injecting device and the receiving unit were disposed at thepositions shown in FIG. 9, and injection of the elastic waves and thereception of the propagation waves were carried out.

[Used Apparatus]

Injecting device: P type Schmitt hammer

Receiver: a cylindrical item (receiver) having a configuration shown inFIG. 31 was attached onto a male screw on a vibration sensor GH-313A(manufactured by Keyence Corporation). The receiver was set and held byhand.

Receiving amplifier: GA-245 (manufactured by Keyence Corporation)

Data logger (recording unit): NR-350 (manufactured by KeyenceCorporation)

[Measurement Result]

Using receivers (Examples 7-1 to 7-3 and Comparison examples 7-1) shownin FIG. 31, the impact elastic wave test was carried out three timeseach, and the difference among the maximum amplitude values wasexamined. The results are in Table 12 and FIG. 32.

As demonstrated in the results shown in the above Table 12 and FIG. 32,by controlling the configuration of the receiver, the inspection usingthe impact elastic waves can be performed for accurate measurement.

Embodiment 8

Referring to FIG. 33, an embodiment of an inspection apparatus forreinforced concrete pipes according to the present invention will bedescribed.

An inspection apparatus shown in FIG. 33 comprises a hammering unittrolley 10, a receiving unit trolley 20, a TV camera trolley 30 and adata recording unit 40. The hammering unit trolley 10, the receivingunit trolley 20 and the TV camera trolley 30 are capable of travelinginside a Hume pipe 100, which is a pipe to be inspected. Thedata-recording unit 40 is disposed above ground within an area to beinspected.

The hammering unit trolley 10 and the receiving unit trolley 20 areconnected to each other with a joint member 50, and it is arranged sothat influence due to vibration generated from the hammering unittrolley 10 at hammering is not rendered to the receiving unit trolley 20side.

It is preferred that the inspection apparatus and the joint 50 are madeof materials such as stainless steel and aluminum alloy, which hardlyaccumulate rust, and are provided with waterproofing characteristic.

As for the connecting method between the joint member 50 and thehammering unit trolley 10 and the receiving unit trolley 20, forexample, the following method may be employed. That is, a connectingfemale screw (not shown) is provided to each of the trolleys 10 and 20,and on the both ends of the joint member 50, a male screw (not shown),which is coupled with the connecting female screw on each of thetrolleys 10 and 20 is prepared respectively, and the male screw at theend portion of the joint member 50 is screwed into the connecting femalescrew on each of the trolleys 10 and 20 to connect to each other.

Also, as another connecting method, an eye bolt is provided to each ofthe trolleys 10 and 20, a hook is provided to both end portions of thejoint member 50, and each of the hooks is hooked to each of the eyebolts on the trolleys 10 and 20 to connect to each other.

Since the distance between the hammering unit trolley 10 and thereceiving unit trolley 20 has to be maintained at a specific distance,the joint member 50 is made of, for example, a material such as metal orresin, which hardly expands and contracts.

The hammering unit trolley 10 and the receiving unit trolley 20 areconnected to each other via an electric cable 60 for data transfer.Also, the receiving unit trolley 20 is connected to the data-recordingunit 40 above ground via the electric cable for data transfer 60.

Mounted on the hammering unit trolley 10 is an injecting device 11 of anelastic wave. The injecting device 11 is disposed on a lifting mechanism12, which is provided with a driving force by means of electric power oran air cylinder. Being driven by the lifting mechanism 12, the injectingdevice 11 can be moved to a position where the hammering is possible atmeasurement. Also, the injecting device 11 can be moved to a positionwhere the injecting device 11 is free from coming into contact with theinner surface of the pipe during traveling.

Mounted on the receiving unit trolley 20 is a receiving unit 21 forreceiving the propagated wave. The receiving unit 21 is disposed on alifting mechanism 22 and provided with a driving force such as electricpower or air cylinder. Being driven by the lifting mechanism 22, thereceiving unit 21 can be raised to a position where the reception ispossible at measurement. Also, the receiving unit 21 can be lowered to aposition where the receiving unit 21 is free from coming into contactwith the inner surface of the pipe during traveling.

The above-mentioned apparatuses such as injecting device 11 and thereceiving unit 21 are securely fixed to each of the trolleys 10 and 20with bolts or the like.

A CCD camera 31 mounted on the TV camera trolley 30 is used fordetermining the elastic wave injecting position by the injecting device11, the elastic wave receiving position by the receiving unit 21 and thereceiving position. The image data from the CCD camera 31 are guided tothe data-recording unit 40 via an electric cable for data transfer (notshown), and displayed on a screen of a monitor 41.

In the embodiment shown in FIG. 33, an example, in which the CCD camera31 is mounted on the TV camera trolley 30, is shown; but it is limitedthereto. The CCD camera may be mounted on any one or both of thehammering unit trolley 10 and the receiving unit trolley 20. Further, itis preferred to mount a lighting apparatus the same as the CCD camera 31for facilitating confirmation of the observation point.

The CCD camera also travels inside the existing conduit. Identical tothe above-described inspection apparatuses and the like, a waterproofingcharacteristic is preferably provided to the CCD camera.

As for the traveling means of the hammering unit trolley 10, thereceiving unit trolley 20 and the TV camera trolley 30 within theconduit, the following methods are conceivable. That is, the TV cameratrolley 30 or the receiving unit trolley 20, which is positioned at thetop, is pulled with a wire or the like; or, the TV camera trolley 30 orthe receiving unit trolley 20 is arranged so as to be self-driven totravel.

Further, it is preferred that, in the hammering unit trolley 10, thedistance from the top of the pipe to the hammering point is maintainedat a fixed distance to stabilize the hammering force provided to theobject to be measured; and thus, to increase the accuracy of theobtained data.

In the embodiment shown in FIG. 33, in the receiving unit trolley 20,the lifting mechanism 22 and the receiving unit 21 are mounted in thisorder on the measuring apparatus main body. However, it is preferredthat, for example, a control mechanism such as a load cell, which iscapable of controlling the contact force of the receiving unit 21, ismounted inside the lifting mechanism 22. Thereby, a constant contactforce can be obtained during measurement resulting in an increasedaccuracy of the obtained data.

Owing to the inspection apparatus having the above-described structure,even when a reinforced concrete pipe of a small diameter into which aninspector cannot enter is inspected, the impact elastic wave test can bereadily carried out.

Here, in the inspection apparatus of the embodiment, by changing (1) thelifting mechanism, (2) the wheel diameter of the trolleys and/or (3) thesize of the trolley, the inspection apparatus of the embodiment can beapplied to the inspection of pipes to be inspected each having adifferent pipe diameter. Further, by adjusting the length of the jointmember 50, the inspection apparatus of the embodiment can be applied tothe inspection of pipes to be inspected each having a different lengthof pipe.

In the embodiment shown in FIG. 33, an example, in which the datarecording unit is disposed above ground, is shown; but is not limitedthereto. The data-recording unit may be mounted on the hammering unittrolley or the receiving unit trolley.

INDUSTRIAL APPLICABILITY

As described above, according to the inspection method of the presentinvention, when inspecting the deterioration state of a reinforcedconcrete pipe constituting a sewage conduit, an irrigation conduit orthe like, the progression level of the deterioration in a componentsegment of an area to be inspected is classified, and a portion to beinspected in detail is selected. Accordingly, the time for inspectionwork can be reduced. Also, the progression level of the deterioration inthe portion to be inspected in detail can be evaluated quantitativelybased on the strength of the pipe. Further, since the magnitude of theprogression level of deterioration can be evaluated quantitatively,based on the strength of the pipe in the portion to be inspected indetail, the strength of the pipe in each of the component segments canbe estimated.

In the inspection method according to the present invention, byarranging to carry out the determination using various data ofdeterioration phenomena such as the area ratio between the highfrequency component and the low frequency component in a resonantfrequency spectrum of propagation waves, the top peak strength ratiobetween a frequency range of 4 to 10 kHz and a frequency range of 3 to 4kHz in the resonant frequency spectrum of the propagation waves, themaximum amplitude value of the propagation waves and decay time of thepropagation waves and the like, the deterioration level of thereinforced concrete pipe constituting the sewage conduit, irrigationconduit and the like can be determined quantitatively. Further, byarranging to carry out the determination while combining those data ofdeterioration phenomena, classification of major deterioration phenomenasuch as axial cracks, peripheral cracks and reduction in thickness ofthe reinforced concrete pipe and the determination of the progressionlevel of the deterioration can be carried out quantitatively.

In the inspection method according to the present invention, by carryingout the impact elastic wave test in a state in which the distancebetween the elastic wave injecting position and the elastic wavereceiving position is ¼ or more of the length of the pipe to beinspected away from each other, the changes of vibration mode due to thedeterioration can be detected precisely.

In the inspection method according to the present invention, by carryingout the impact elastic wave test using a receiver of which the front endis a cone-like shape or needle-like shape, a receiver of which front endsurface is flat and the area of the front end surface is 3 cm² or less,or a receiver of which the front end surface is a curved surface and thecurvature radius of the front end surface thereof is 25 mm or less asthe receiver of the elastic waves, the inspection by means of the impactelastic wave test can be carried out accurately irrespective of thestate of the inner surface layer of the pipe to be inspected.

According to the inspection apparatus of the present invention, evenwhen inspecting a reinforced concrete pipe having such a small diameterthat an inspector or the like cannot enter thereinto, the inspectionmethod having features as described above can be carried out readily.

TABLE 1 Classification of Sample Resonant frequency deterioration T110.8 KHz 3 T12 0.2 KHz 1 T13 0.5 KHz 2

TABLE 2 Sample T21 Sample T22 Sample T23 Sample T24 Non-processed ItemItem Pipe with item introduced introduced ground inner with 4 axial with10 axial surface cracks cracks

TABLE 3 Area ratio calculation result of each sample Sample T21 T22 T23T24 0 to 4 KHz 32% 47% 73% 55% 4 to 8 KHz 68% 53% 27% 45%

TABLE 4 Sample T31 Sample T32 Sample T33 Non-processed item Itemintroduced with Item introduced with peripheral crack: peripheral crack:0.15 mm 1.3 mm

TABLE 5 Peak strength ratio calculation result Sample T31 T32 T33 Peakstrength 0.97 1.40 1.57 ratio

TABLE 6 Sample T41 Sample T42 Sample T43 Sample T44 Sample T45Non-processed Item Item Item Item item introduced introduced introducedintroduced with 4 with 10 with with axial axial peripheral peripheralcracks cracks crack: crack 0.15 mm 1.3 mm

TABLE 7 Maximum amplitude value (output value of receiving unit [v]) ofeach sample Sample T41 Sample T42 Sample T43 Sample T44 Sample T45 14.010.8 7.1 11.0 8.3

TABLE 8 Deterioration Pipe with reduced Peripheral phenomena thicknesscrack Axial crack Maximum amplitude No change Reduction Reduction valueDecay time No change No change Reduction Area ratio High frequency Nochange High between an area of component is frequency high frequencyreduced. component is component and an reduced. area of low frequencycomponent Top peak strength Strength in the Strength in the No change inthe frequency low frequency high frequency range of 4 to 10 kHz side issmall. side is large. and top peak strength in the frequency range of 3to 4 kHz

TABLE 9 Sample T51 Sample T52 Sample T53 Sample T54 Sample T55 SampleT56 Non-processed Item Item Item Item Pipe item introduced introducedintroduced introduced with with 4 axial with 10 axial with with groundcracks cracks peripheral peripheral inner crack: 0.15 mm crack 1.3 mmsurface

TABLE 10 Maximum amplitude value (output value of receiving unit [v]) ofeach sample Sample Sample Sample Sample Sample Sample T51 T52 T53 T54T55 T56 14.0 10.8 7.0 11.0 8.3 13.8

TABLE 11 Comparison Comparison Example 6-1 Example 6-2 Example 6-3Example 6-4 Example 6-5 example 6-1 example 6-2 Distance between 800 400350 300 270 200 20 the injection and the reception (mm) No deterioration14.0 13.5 14.0 13.5 14.0 13.5 13.9 Item introduced 7.1 11.0 10.0 11.912.0 13.1 13.5 with crack

TABLE 12 Comparison Example 7-1 Example 7-2 Example 7-3 example 7-1 (a)Measurement results of sample with reduced pipe thickness 1st 12.8313.03 13.13 3.81 2nd 12.53 12.53 12.73 1.90 3rd 12.53 12.73 12.83 12.73(b) Measurement results of sample applied with lard 1st 12.79 12.4512.98 12.56 2nd 12.56 12.78 12.78 11.79 3rd 12.91 12.56 12.63 6.12

1. A method of inspecting a reinforced concrete pipe to determine astate of deterioration inside the pipe, comprising: performing an impactelastic wave test in a state in which a distance between an elastic waveinjecting position and an elastic wave receiving position is at least ¼of a length of the pipe to be inspected, wherein said impact elasticwave test is performed by using a receiver having a flat front endsurface to receive elastic waves, an area of the front end surface beingno greater than 3 cm².
 2. A method of inspecting a reinforced concretepipe to determine a state of deterioration inside the pipe, comprising:performing an impact elastic wave test in a state in which a distancebetween an elastic wave injecting position and an elastic wave receivingposition is at least ¼ of a length of the pipe to be inspected, whereinsaid impact elastic wave test is performed by using a receiver having acurved front end surface to receive elastic waves, a radius of curvatureof the front end surface being no greater than 25 mm.
 3. The inspectionmethod of claim 1, further comprising using an inspection apparatus toinspect the pipe, the inspection apparatus including: a first trolleyhaving a hammering unit; a second trolley having a receiving unit; and ajoint member for connecting the first trolley and the second trolley sothat the first trolley and the second trolley are spaced apart.
 4. Theinspection method of claim 3, further comprising using the inspectionapparatus to determine the elastic wave injecting position and theelastic wave receiving position by mounting a TV camera on one of thefirst trolley and the second trolley.
 5. The inspection method of claim2, further comprising using an inspection apparatus to inspect the pipe,the inspection apparatus including: a first trolley having a hammeringunit; a second trolley having a receiving unit; and a joint member forconnecting the first trolley and the second trolley so that the firsttrolley and the second trolley are spaced apart.
 6. The inspectionmethod of claim 5, further comprising using the inspection apparatus todetermine the elastic wave injecting position and the elastic wavereceiving position by mounting a TV camera on one of the first trolleyand the second trolley.